dna
In 1966, Francis Crick proposed the Wobble Hypothesis which explained that the degeneracy of the genetic code is caused by the structure of the anticodon of tRNA. The anticodon is a three base sequence on the tRNA complementary to the codon on the mRNA. Each tRNA binds to a specific amino acid, but the anticodons of some tRNA molecules can bind to two or three different codons. This flexibility of the anticodon is caused by the less stringent 5' base on the anticodon loop, also referred to as the wobble base, which binds to the 3' base on the mRNA. Only the first two nucleotides are stringent and spatially confined for the decoding of the mRNA codon into an amino acid. This explains why degenerate codons often differ in the third position, as depicted in Figure above . For example, the amino acid alanine is coded by codons GCU, GCC, GCA and GCG. The wobble movement of the base in the 5' anticodon position is necessary for this degenerate capability.